This application relates to passive temperature compensators, and more specifically, to passive temperature compensators used in fiber-based devices and systems.
Various materials change their physical dimensions with a change in temperature. In many devices and systems, such temperature dependency is undesirable because it may adversely alter the characteristics or performance of a device. For example, this temperature dependency of an optical path in an optical device may change the associated optical path length and hence introduce a temperature-dependent phase shift in an optical signal propagating along the path. This phase shift can degrade the performance or even interrupt the normal operations of the device.
Examples of optical devices and systems that are sensitive to such temperature dependency include, among others, devices based on optical interference. Optical resonators or cavities, for example, are sensitive to a change in the optical path length. A laser""s main component is its optical cavity that encloses a laser gain medium. The simplest-optical cavity includes two reflectors to reflect light between them. The laser cavity provides an optical feedback mechanism to bounce light back and forth multiple times through the laser gain medium for optical amplification. The laser cavity also selects one or more proper lasing frequencies within the gain spectral profile of the laser gain medium by requiring each selected frequency of light to be in resonance with the laser cavity. Furthermore, the laser cavity operates to confine the light rays of the laser approximately along the optic axis of the laser cavity by filtering out light rays in other directions. As a result, the geometry of the laser cavity affects various characteristics of the laser.
The geometry of the laser cavity, however, may change with respect to many factors, such as environmental conditions (e.g., temperature or vibrations) and its own aging process. One notorious factor is a change in the cavity length due to the thermal expansion. Since a change in the laser cavity is time dependent, it is therefore desirable to provide an active control mechanism to stabilize the laser cavity by dynamically adjusting the optical path length of the cavity to mitigate variation in the optical path length of cavity caused by temperature, vibration, or aging of the cavity.
A device according to one embodiment includes an inner hollow cylindrical member and an outer hollow cylindrical member engaged to each other as a passive thermal compensator. The inner hollow cylindrical member is formed of a first material with a first coefficient of thermal expansion and has a gap along a cylindrical axis to split the inner hollow cylindrical member. The outer hollow cylindrical member is formed of a second material with a second coefficient of thermal expansion greater than the first coefficient of thermal expansion and havs a gap along a cylindrical axis to split the outer hollow cylindrical member. The inner hollow cylindrical member is situated within the outer hollow cylindrical member and has an outer surface conformingly engaged to an inner surface of the outer hollow cylindrical member. A fiber loop may be wound around the outer hollow cylindrical member so as to reduce a thermal variation in the fiber length.